Science Inventory

Mechanisms of Phosphorus Removal by Phosphorus Sorbing Materials

Citation:

Zhixuan, Q., A. Shober, K. Scheckel, C. Penn, AND K. Turner. Mechanisms of Phosphorus Removal by Phosphorus Sorbing Materials. JOURNAL OF ENVIRONMENTAL QUALITY. American Society of Agronomy, MADISON, WI, 47(5):1232-1241, (2018). https://doi.org/10.2134/jeq2018.02.0064

Impact/Purpose:

Core ideas: • P speciation of PSMs was determined using XANES for stormwater filtration structure. • Evaluated PSMs removed P via Al/Fe sorption, Ca sorption, or both mechanisms. • P speciation is valuable in guiding the selection of PSMs for stormwater filtration structure. The objective of this research is to determine the mechanisms of P removal by phosphate sorbing materials (PSMs) used in stormwater P filtrations structures using XANES spectroscopy to estimate the efficacy of various PSMs as filter media.

Description:

Stormwater filters are a structural best management practice designed to reduce dissolved P losses from runoff. Various industrial byproducts are suitable for use as P sorbing materials (PSMs) for the treatment of drainage water; P sorption by PSMs varies with material physical and chemical properties. Previously, P removal capacity by PSMs was estimated using chemical extractions. We determined the speciation of P when reacted with various PSMs using X-ray absorption near edge structure (XANES) spectroscopy. Twelve PSMs were reacted with P solution in the laboratory under batch or flow-through conditions. In addition, three slag materials were collected from working stormwater filtration structures. Phosphorus K-edge XANES spectra were collected on each reacted PSM and compared with spectra of 22 known P standards using linear combination fitting in Athena. We found evidence of formation of a variety of Ca-, Al-, and/or Fe-phosphate minerals and sorbed phases on the reacted PSMs, with the exact speciation influenced by the chemical properties of the original unreacted PSMs. We grouped PSMs into three general categories based on the dominant P removal mechanism: (i) Fe- and Al-mediated removal [i.e., adsorption of P to Fe- or Al-(hydro-)oxide minerals and/or precipitation of Fe- or Alphosphate minerals]; (ii) Ca-mediated removal (i.e., precipitation of Ca-phosphate mineral); and (iii) both mechanisms. We recommend the use of Fe/Al sorbing PSMs for use in stormwater filtration structures where stormwater retention time is limited because reaction of P with Fe or Al generally occurs more quicklythan Ca-P precipitation.